Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2000-07-25
2001-11-27
Masih, Karen (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S434000, C318S132000, C318S606000, C318S798000, C318S812000, C318S811000
Reexamination Certificate
active
06323610
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improvements in methods and circuits for driving DC brushless, polyphase motors, such as a spindle motor of a hard disk drive, or the like, and more particularly to improvements in such driving methods and circuits that at least reduce the acoustic noise in motors of this type, and to improvements in driving methods and circuits for driving such motors using driving voltages that are approximations of waveforms constructed from substantially sinusoidal waveform segments, and, more particularly, constructed from substantially linear approximations of such waveform approximations.
2. Relevent Background
In the operation of DC brushless, polyphase motors of the type to which the invention pertains, efficient motor drive requires that the excitation current applied to the motor phases be aligned with the bemf generated by individual phases. One of the best schemes for achieving this alignment is the use of a phase-locked loop (PLL), which adjusts the phase and frequency of the commutation, so that the bemf of the undriven winding passes through zero in the center of the appropriate commutation state. This scheme works well when the shape of the commutation waveforms includes an undriven region, as in a conventional 6-state, +1, +1, 0, −1, −1, 0, sequence.
Since the +1, +1, 0, −1, −1, 0 sequence has sharp transitions between driving states, this sequence has many high frequency components. These tend to excite mechanical resonances in the motor, which results in the creation of undesirable acoustic noise. Moreover, the step-function tristating of the undriven motor phases, together with the step-function driving waveform itself produces a degree of torque ripple in the motor. The torque ripple results in an unevenness or jerkiness in the motor rotation, which also excites resonances in the motor, also causing undesirable acoustic noise.
Thus, if it is desired to reduce acoustic noise, a sine wave shaped excitation signal is more appropriate than the 6-state sequence. If the motor driver consists of sinusoidal current sources, the same voltage sensing PLL described above can be used. However, when the duty cycle of the driver is varied sinusoidally, the motor driver excitation is pulse-width modulated (PWM) to minimize power dissipation in the driver IC. This permits lower cost packaging and an overall saving in system cost. However, in the past, it has been difficult to generate currents that have a pure sinusoidal waveform, particularly when the currents are relatively high, and when a PWM scheme is desired to be used.
In previous application Ser. No. 09/300,754, after initial baseline cancellation, a driving waveform was formed of concatenated segments of 120° of zero, followed by 120° of “up hook”, and 120° of “down hook”. The up-hook and down-hook waveforms were generated in two MDACS. The operation of the MDACs had some problems that resulted in difficulty in forming the desired driving waveforms. In particular, circuit tradeoffs needed to be made so that the resulting waveforms could properly operate in the polyphase DC motor environment.
Also, using an MDAC to form waveforms segments that are themselves formed from sinusoidal waveforms segment combinations requires special MDAC design and operational considerations. A design in which the driving waveforms can be constructed from linear waveform segments to approximate the sinusoidal waveforms segment combination would significantly ease the realization and operation of such MDAC.
Consequently, what is needed is a disk drive and method for operating it in which the noise associated with the drive in operation is reduced or eliminated. What is additionally needed is a disk drive and method that employs drive signals that are developed from sinusoidal signal segments, which can be easily approximated and generated by concatenated linear signal segments.
SUMMARY OF THE INVENTION
In light of the above, therefore, it is an object of the invention to provide an improved disk drive and method for operating it in which the noise associated with the drive in operation is reduced or eliminated.
It is still another object of the invention to provide a disk drive and method that employs multiple drive signals that have segments that have substantially continuously concatenated waveforms that are constructed from or which approximate segments of a sinusoidal signal.
These and other objects, features and advantages of the invention will be apparent to those skilled in the art from the following detailed description of the invention, when read in conjunction with the accompanying drawings and appended claims.
Thus, according to a broad aspect of the invention, a method is presented for operating a three-phase dc motor. The method includes generating a set of three waveforms to provide drive voltages to respective windings of the motor. Each waveform has period of 360°, with a first segment having a value of zero for 120°, followed by a second segment having an “up slope” shape for 60°, followed by a third segment having two consecutive “cap” shapes for 120°, followed by a fourth segment having “down slope” shape for 60°. Each waveform of the set is displaced from one another by 120°. The waveforms are then applied to the respective windings of the motor. The segments each approximate VMAG(sin(&ohgr;t−&phgr;)−min{sin(&ohgr;t), sin(&ohgr;t−120°), sin(&ohgr;t−240°)}, where VMAG is the peak amplitude of each waveform, &ohgr;t is a phase angle of the waveform, and &phgr; is an initial phase angle; however, in a preferred embodiment, the waveform segments comprises at least one linear waveform. Preferably, the waveform segments may have two linear portions, with a breakpoint at a midpoint section thereof.
According to another broad aspect of the invention, a method for reducing acoustic noise in operating a polyphase dc motor is presented. The method includes generating a set of n waveforms to provide drive voltages to respective windings of the motor, n being the number of phases of the polyphase dc motor. Each waveform has period of 360°, and has a first segment value of zero for (360
)°, a second “up slope” segment for (360/2n)°, a third segment with two consecutive “cap” shapes for (360
)°, and a fourth “down slope” segment for (360/2n)°. Each waveform of the set is displaced from one another by (360
)°. The waveforms are applied to the respective windings of the motor to energize it. The waveforms may be pulse-width modulated prior to application thereof to the drivers.
Each of the segments may approximate VMAG(sin(&ohgr;t−&phgr;)−min{sin(&ohgr;t−0×360
)°, sin(&ohgr;t−1×360
)°, . . . sin(&ohgr;t−(n−1)×360
)°}), where VMAG is a maximum amplitude of each waveform, n is a number of phases of the motor, &ohgr;t is a phase angle of the waveform, and &phgr; is an initial phase angle. The waveform segments may comprise at least one linear waveform, and more particularly may have two linear portions, with a breakpoint at a midpoint section thereof.
According to yet another broad aspect of the invention a circuit is presented for operating an n-phase dc motor. The circuit has drivers for applying n driving signal waveforms to the motor. A source of the driving signal waveforms is provided. Each of the driving signal waveforms has a period of 360° with a first segment having a value of zero for (360
)°, followed by a second segment having an “up slope” shape for (360/2n)°, followed by a third segment having two consecutive “cap” shapes for (360
)°, followed by a fourth segment having a “down slope” shape for (360/2n)°. Each waveform of the set is displaced from one another by (360
)°. The driving signal waveforms may include substantially linear segments, and, more particularly, may have two linear portions, with a breakpoint at a midpoint thereof. A circuit may also be provided for pulse-width modulating the driving signal
Ng Vincent
White Bert
Brady W. James
Masih Karen
Swayze, Jr. W. Daniels
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
LandOfFree
Silent spin sine wave generator does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Silent spin sine wave generator, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Silent spin sine wave generator will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2585801